1. Field of the Invention
The present invention relates to a process for converting iron-containing reactor feed into iron carbide, which is useful in the direct production of steel. More particularly, the present invention relates to controlling the conversion of reactor feed into iron carbide to assure that a suitable iron carbide product is produced.
2. Description of the Related Art
Typically, iron ore is converted to steel through a basic process that has been in use for many years. This process involves the conversion of iron ore to pig iron in a blast furnace using coke produced in a coke oven and the subsequent conversion of the pig iron to steel in an open hearth or basic oxygen furnace. However, this process has a number of drawbacks, some of which have been brought about by realities of life in the late twentieth century. For example, due to environmental standards, capital costs involved with the construction of a steel mill which meets pollution standards or the modification of existing plants to meet pollution standards would now be prohibitive. When the capital costs are factored into the price that must be charged for the steel produced by such a steel mill, the price of that steel would simply not be competitive on the world market. Additionally, the traditional steel-making process is energy intensive, and energy costs involved with making steel in the traditional manner have become excessive. With the availability and cost of energy in the near future being unpredictable, the traditional manner of manufacturing steel faces an uncertain future.
Accordingly, a demand has been created for relatively clean, energy efficient and less expensive methods for producing steel. In this regard, a great deal of effort has been directed to the elimination of the blast furnace and the coke oven in steel-making. Blast furnaces and coke ovens are inefficient, consuming large quantities of energy, and are responsible for a large portion of the pollution involved with steel-making. In this effort, some attention has been directed to the conversion of iron ore directly to iron carbide followed by the production of steel from the iron carbide, thereby eliminating the use of the blast furnace and the coke oven.
In this regard, U.S. Pat. No. Re. 32,247 by Stephens, Jr., dated Sep. 16, 1986, a reissue of U.S. Pat. No. 4,053,302 by Stephens, Jr. issued Oct. 11, 1977, discloses a process for the direct production of steel. Iron-containing reactor feed is converted to iron carbide, and steel is then produced directly from the iron carbide in a basic oxygen furnace or an electric arc furnace. In the converting step, the iron oxide in the reactor feed is reduced and carburized in a single operation using a mixture of hydrogen as a reducing agent and carbon-bearing substances as carburizing agents. The blast furnace step of traditional steel-making techniques is eliminated, as steel is then produced by introducing the iron carbide into a basic oxygen or electric arc furnace.
This method of directly producing steel represents a significant advance in the art. However, improvements in the method have proven desirable. It has been found that in the step of converting the reactor feed into iron carbide, even minor variations in the process parameters, which include pressure, temperature, and individual gas concentrations in the process gas, cause inferior results. That is to say, minor variations in any process parameter can cause free iron (Fe) or one of a variety of iron oxides, such as Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4 and FeO, to be included in the iron carbide product.
Therefore, there are significant problems associated with ensuring a suitable iron carbide product. Also, significant problems have been encountered in converting reactor feed into iron carbide at an acceptably high rate. Slow conversion of reactor feed to suitable iron carbide product can severely impair the commercial viability of a process.
As can be seen, a significant need exists for a process for producing a high quality iron carbide product at an acceptable conversion rate.